Pandion Haliaetus (Osprey)

The Osprey (Pandion haliaetus) also called sea hawk, river hawk, and fish hawk is a diurnal, fish-eating bird of prey with a cosmopolitan range. It is a medium raptor, reaching more than 60 cm (24 in) in length and 180 cm (71 in) across the wings. It is brown on the upperparts and predominantly greyish on the head and underparts.

Physical Description

Ospreys are large birds of prey (55 to 58 cm long), with a wingspan ranging from 145 to 170 cm. Their long wings have a characteristic bend at the carpal ("wrist") joints. They are bright white underneath, with dark brown patches at the carpal joints and a mottled dark brown necklace. Other identifying markings include a dark stripe through each eye, and a dark brown back. The feet of this species are pale blue-gray, and the beak is black. Juvenile ospreys resemble adults, but have a somewhat speckled appearance due to buff-colored tips on their dark brown upper-wing and back coverts and a less well-defined necklace. Juveniles also have an orange-red iris, rather than the yellow iris that is typical of adults. Juvenile plumage is replaced by adult plumage by 18 months of age.

On average, while not necessarily longer, female ospreys are 20% heavier than males and have a wingspan that is 5 to 10% greater. In North America, for example, male ospreys range in mass from 1200 to 1600 g, whereas females range from 1600 to 2000 g. Female ospreys also often have darker plumage and a more defined necklace than their male counterparts.

Ospreys display morphological variation by region. Tropical and subtropical individuals tend to be smaller than individuals that breed at higher latitudes. The four subspecies of ospreys show some variation in size and color. Pandion haliaetis haliaetus and P.h. carolinensis are the largest and darkest subspecies. P.h.ridgwayi is approximately the same size as carolinensis, but is paler on the head and breast. P.h. cristatus is the smallest subspecies, with a dark necklace and pale crown.

Ospreys have several morphological adaptations to their unique fish-eating lifestyle. These adaptations include relatively long legs for a raptor, spiny footpads called spicules, long, sharp, curved claws, and a reversible outer toe to aid in gripping slippery fish. In addition, ospreys have dense oily plumage and efficient nasal valves that prevent water from entering the nostrils when the bird dives to catch a fish.

Geographic Range

Ospreys have a worldwide distribution, wintering or breeding on every continent except Antarctica. Ospreys are not known to breed in South America or Indo-Malasia, but are sometimes found there in the winter. Ospreys are winter breeders in Egypt and some Red Sea islands. Regions where ospreys are particularly abundant include Scandinavia and the Chesapeake Bay region of the United States.

There are four subspecies of ospreys, which are separated by geographic region. Pandion haliaetus carolinensis breeds in North America and the Caribbean, and winters in South America. P. h. haliaetus breeds in the Palearctic region (Europe, north Africa and in Asia, north of the Himalayas) and winters in south Africa, India and the East Indies. P. h. ridgwayi is a non-migratory subspecies. It resides in the Caribbean, with a range that extends from the Bahamas and Cuba to southeast Mexico and Belize. The final subspecies, P. h. leucocephalus is also a non-migratory subspecies. Its range includes Australia and the southwest Pacific.

Habitat

Ospreys have a wide distribution because they are able to live almost anywhere where there are safe nest sites and shallow water with abundant fish. Nests are generally found within 3 to 5 km of a water body such as a salt marsh, mangrove (Rhizophora) swamp, cypress (Taxodium) swamp, lake, bog, reservoir or river. The frequency with which each of these habitat types is used varies by geographic region.

Ospreys choose structures that can support a bulky nest, and that are safe from ground-based predators. Nest sites can be safe from predators either by being difficult for a predator to climb (e.g. on a cliff) or by being over water or on a small island. Over-water nest sites that are often used by ospreys include buoys and channel markers, dead trees and artificial nest platforms. Ospreys have also been known to nest on various man-made structures, such as power poles, duck blinds, communication towers, buildings and even billboards. In many cases, nests that are built on artificial structures such as nest platforms and power poles are more stable and fledge more chicks per breeding season than nests on naturally-occuring structures.

Justification (IUCN Red List)

This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (extent of occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be increasing, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over 10 years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in 10 years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.

Ospreys mate for life. In Finland, they arrive from migration around mid-April after wintering in Africa, and settle on their nests. Markus varesvuo took this picture on the couple’s first day back.

Location: Vaala, Finland (photographed from a hide)

Photo info - 28.04.2016: Canon EOS-1D X, 1200 mm, ISO 1600, f 11, 1/500 sec, Flash: not used

Tags: bird photography, markus varesvuo, osprey, pandion haliaetus